This invention relates to bows for archery and, in particular, to a pivoting pocket attached to the bow handle for holding a bow limb in place.
Archery bows are available in a variety of forms. Long bows, recurve bows, compound bows and others are all basically intended to propel an arrow through the flecture of limbs that transfer the stored energy through such flecture to the arrow through a bow string. The present invention is directed to the attachment of flexible limbs to a handle portion of such bows. For example, a recurve bow may incorporate a rigid handle section to which an opposing pair of flexible limbs are secured in a manner unique to recurve bows and familiar to those in the archery industry. Similarly, a compound bow is provided with a rigid handle portion to which flexible limbs are secured; long bows and similar types of archery bows are usually constructed with the handle and limbs formed in a unitary structure without a discernibly separate handle portion or limbs. This invention is directed to those archery bows wherein the limbs are separable from the handle and is specifically directed to overcome the difficulties that may be encountered in the manufacture, mounting, adjustment, and use of limbs attachable to a bow handle.
Compound bows differ from most other bows in that they include wheels or cams (referred to herein as "eccentrics") attached at the free ends of the limbs to obtain a mechanical advantage in bending the bow. Typically, two eccentrics are used, with lacing wound from an anchor at one end of a first limb to the eccentric at the end of the other limb, to the eccentric at the first end, then back to an anchor at the other end. The middle span between the eccentrics contains the serving or region for receiving the nock of the arrow. As used herein, "lacing" can refer to a single piece bowstring or a three piece line comprising two end cables connected by a central stretch between the eccentrics which forms the bowstring. For convenience, the terms may be used interchangeably herein.
Attachment of the limbs to the handle of a compound bow may be particularly critical since the utilization of eccentrics at the outer ends of the limbs usually presents a means for increasing the mechanical advantage and the multiplication of force applied to the limbs, which force is transferred to the handle through the attachment between the limbs and the handle. The prior art, such as represented by U.S. Pat. No. 4,261,320, typically provides a pivot at each end of the handle of a compound bow. The pivot includes a semicircular groove in each end of the handle, perpendicular to the length of the handle. Each limb rests on the flat side of a half-round member near the fixed end of the limb. The curved side of the half-round member rides in the semicircular groove. The sides of the handle extend past the sides of the limb to form a partial pocket. This configuration limits the choice of materials for the pivot. A handle typically comprises aluminum or magnesium, relatively soft materials. A limb typically comprises fiberglass. The half-round member typically comprises a hard plastic. The resulting joint between the limb and the handle is not particularly strong or durable since the bearing material of the pivot comprises the soft metal of the handle and the half-round member of plastic.
In such prior art, the limb extends over the pivot and is attached at its end to the handle. The pivot acts as a fulcrum across which the limb bends as the bowstring is drawn. A bolt attaches the end of the limb to the handle. The bolt is longer than necessary merely to fasten the limb to the handle so that the bolt also provides a means for adjusting the force necessary to draw the bowstring by changing the angle between the handle and the limb. Typically, the bolt is of sufficient length that, when the bolt is unscrewed, the limb is unflexed prior to the bolt becoming fully withdrawn. This enables one to "relax" the bow, for bowstring replacement for example.
Because of the use of stiff limbs in compound bows, the forces on the handle can be considerable. The forces are further increased due to the cams or eccentric wheels which enable one to use a much higher maximum draw weight. The force of the bowstring acting on the end of the limb may not align with the mounting of the limb to the handle, e.g. because of the way the bowstring is statically mounted or because of a sideward force from using a finger release or a sideward force due to the cable guard. The result is a force tending to move the limb from side to side as the bow is held by the archer. Thus the mounting of the limb must be substantial enough to resist these forces so that the bow performs consistently.
Simply making the handle thicker will make it more substantial, but at increased cost to manufacture. The basic difficulty is that limb and handle meet in orthogonal planes. That is, the handle is wider front to rear, as held by the archer, and the limb is wider from side to side. Making pockets as part of the handle requires that the starting billet be substantially thicker than the final thickness of the handle in order to have adequate material for the pockets. This increases the amount of material which must be used and increases the amount of material which must be machined (removed) to form the central portion of the handle.
Canadian Patent 747,692 discloses a take-apart long bow having pivotally adjustable limb portions in separate pockets. A central bore contains a pivot pin and one of three surrounding bores receives a lock pin. Such construction is not adaptable to compound bows because the joint cannot take the forces encountered in a compound bow. Further, even if adaptable, the draw/weight adjustment is incremental, not continuous, in the bow described in the Canadian patent. Continuous adjustment is desirable and necessary in a compound bow since many or most users prefer that the tiller measurements (perpendicular distance from bowstring to one end of handle) be slightly different (about 1/8 inch) for the upper and lower limbs in a compound bow. A change that small would be virtually impossible to obtain with an incrementally adjustable bow.
In view of the foregoing, it is therefore an object of the invention to provide an improved means for securing the limbs to the handle of archery bows.
A further object of the invention is to provide an improved archery bow in which the limbs are secured to the handle through the use of pivoting pocket members.
Another object of the invention is to provide pocket members for receiving and securing the ends of the limbs of a bow to the bow handle.
A further object of the invention is to provide an improved archery bow in which the components for attaching the limbs to the handle can be of different material from the handle.
Another object of the invention is to facilitate the manufacture of a bow handle from less material when the handle is to be machined.